Such a filter device is known from U.S. Pat. No. 3,637,079. In this publication a filter device comprising multiple filter candles, vertically suspended from a wall plate in a funnel-shaped tank are shown, for filtering fluids that are supplied to a lower side of the tank. The outflow side of the filter candles can for cleaning be flushed in reverse flow with water with bacterial or cleansing additions, from a container that is connected via a feed pipe and a shutoff valve to the outflow side of the filter candles. A compressed air unit is connected to the container to pressurize the cleaning fluid. The volume occupied by the cleaning fluid is less than half the total volume of the container. Upon flushing of the filter candles, the pressure in the pressure vessel drops to about 3.5 bar. After the cleaning fluid has, upon opening of the shutoff valve, has flowed into the filter candles and has formed a film of fluid on the inner walls of the filter candles, the compressed air from the container passes into the filter candles. The sludge attached to the outside of the filter candles is thereby loosened and slides away into the funnel-shaped base of the tank. The known filter device has as a disadvantage that the compressed air unit requires a relatively large amount of energy. Furthermore, after a cleaning operation, it will take a relatively long time pressurizing the cleaning fluid container after its refilling.
Another filter device is described in WO 03/020397. In this document a filter backflushing system is described including an accumulator containing a pressurised bladder which propels a supply of backwash fluid contained within the accumulator in a reverse direction a filter element. The volume of backwash fluid that is displaced by the bladder will be relatively small, such as several liters, as reliable membranes that can displace fluids at high pressures are of relatively small-size. Furthermore, the use of a flexible bladder will lead to a limited operating life and to susceptibility of the system to failure or leakage.
It is therefore an object of the invention to provide a filter device and method of cleaning such a filter device, which effectively transports large volumes of cleaning fluids through a filter at increased pressure, requiring relatively little energy. It is a further object of the invention to provide a filter device and method of cleaning, which filter device can be rapidly brought into the operational state after a cleaning operation.